Electrical musical instruments



Feb. 27, 1962 R. H. DoRF 3,022,696

ELECTRICAL MUSICAL INSTRUMENTS Filed Jan. 29, 1957 2 Sheets-Sheet 1 /NvE/vrof? Richard H. Dorf by L/ Avro NEY Feb. 27, 1962 R. H. DoRF ELECTRICAL MUSICAL INSTRUMENTS 2 Sheets-Sheet 2 Filed Jan. 29, 1957 .vdi

m. v E T wm A E NN INVENTOR Rlchord H Dorf h foam-:Y

aired States This invention relates to velectrical musical instruments and particularly to apparatus for producing percussive sounds in such instruments.

Percussive devices for electrical musical instruments generally have means for modifying the it-'ave form of the output tones emitted by the instrument in such a manner that the attack and decay characteristics kof the modified tone resemble those of struck or plucked instruments rather than the continuous tone oforgans and bowed or blown musical instruments. Such a percussivewave form is generally characterized by having a sharp attack or steep wave front, followed by a gradual but/definite decay in amplitude. v

fit is, therefore, an object of 4fthe invention to -provide a percussion systemv for electrical musical instruments which allows a succeeding note to be `played with a percussive lattack and decay regardless of whether previously lstruclckey's are held down vor released.

It isenother object of the invention to provide apparatus for controlling the attack and decay envelope or" the emitted tones of an electrical musical instrument which may -be added as a se arateunit 'to the instrument with which it is adapted to be associated without the necessity of alteration thereto. v

it -is still a further object of the `invention to `provide a percussive envelope control system for an electrical musical instrument which requires no key switches when associated with a keyboard instrument other than those normally necessary for continuous tone playing.

lt is a further object of the invention to provide a percussion system for electrical-musical instruments having means for selectively terminating the decay period of each `successive note upon release of a key associated with cach note.

it is yet another object of this invention to provide a percussion system for electrical ymusical instruments having means for repeating each y'percussive tone at a rapid rate for yseveral cycles cach time the system is operated.

it isa further object of the invention to provide apparatus for controlling the attack and decay envelope of vthe `emitted tones oi' an electrical lmusical instrument which utilizes an envelope control amplifier valve as a device for shaping the -decay portion of the tone envelope. .For a better understanding -of the invention, together with other and `further `objects thereof, reierenceis made to the following detailed description taken in connection with'the accompanying drawings, in which:

l illustrates in box schematic diagram form a vvpreferred embodiment of they invention.

FIG. 2 is an electrical circuit diagram of an embodi- -nient of the invention.

FIG. 3 is an electrical circuit diagram of a modifica tion of the invention.

FiG. 4 is an electrical circuit diagram of another ein bodiment of the invention.

Referring now to the drawings, the embodiment of the invention shown in FIGA, in general, has a pair oi' input terminals 1l) which .may be connected to anysource of electrical audio signal. it will be 4understood that although .tlie present invention is shown and described by `way oi' example-,in association with ka keyboard operated,

continuous tone instrument, such as an electronic organ; yet, -as the V system .is adapted-to .be `connectedto the outlil pnt of any tone generating device, it may be used with any other type of continuous tone, electrical musical instrument. The terminals 10 may be connected directly to the output of the instrument, although, if desired, they may be connected to some intermediate point in the circuitry of the instrument and preferably at a point where the original complex generated wave form exists and be- `fore the introduction of formant i'ilters or other wave changing circuits.

ri`erminals 1i! are connected to a signal amplifier 12 where the signal is ampli'ded and then fed to u rectiiier filter circuit 14. lRectifier 14 may be any well-known rectifier circuit such as a half-wave diode circuit which is followed by a filter having a time constant of suiiicient length to substantially eliminate any existing ripple at the lowest tone frequencies to be used, yet not of -suilicient length to delay the rise of the resulting DC. voltage to a maximum level. The output of 'rectifier-filter 14 is substantially `D.C. and is applied to a circuit comprising capacitor lo and resistor 18 which is connected to the grid of a puise amplifier -20 and constitutes a 'differentiation circuit. Ulfifnen asigna-l is applied to terminals il), a DC.

'volt-age appears at the output of rectiier-iilter 14. The

leading edge of the D.C. wave causes a sharp pulse lo be passed through the diierentiator lcomponents 16, 1S to the input of pulse amplier 20. At the Aconclusion of the pulse, no further signal can appear at the input of pulse amplifier 2) as capacitor A16 cannot carry -D.C., even though the player may continue to 'hold down a key -or otherwise feed a continuous tone to terminals 10, thereby causing direct current to remain lat the output of rectiiler i4.

The pulses `are amplified by puiseainplitier 20 and pass through coupling capacitor 22 to a relay :amplifier 24. Amplier 24 comprises an electronic valve in Whose output circuit a normally open relay 26 is connected so that when a pulse appears at the input of relay amplifier 24, the normally open contacts of relay 26 close but remain closed only for the duration of the narrow pulse fed from pulse ampliiierll and open when the-pulse ends. A suitable DC. voltage from `D.C. supply 28 is connected to one of the relay contacts and the other contact is so connected that when the contacts are closed, the DE. voltage from supply 28 is Lapplied to a capacitor 30 with associated bleeder resistor 32, both of which .are connected to the input of an intensity envelope control 'amplifier 34, which controls the Vmagnitude or intensity of the output signal. The D.C. voltage from supply 2S applied by relay 26 charges capacitorv 30 almost immediately.

When the relay conta-cts open a't the conclusion of the actuating pulse, the capacitor 36 begins to discharge 'through resistor 3f. at a rate determined by the time coustant of the capacitor-resistor circuit. Capacitor 30 is connected to one oi the control electrodes of envelope control amplifier '34 in such a manner that 'when it is charged, the ampliiier operates. As capacitor 30 'discharges, the amplifier output decreases proportionately until the cutofipointisreached.

For purposes 'o illustration .the same signal source, from 'which 4the triggering pulse .is developed, is applied to amplier 3aby'means of a line 37 connected to terminais lil. However, it will be understood that the input signal applied to terminals 10 and the signal applied to amplifier 34 may originate from entirely separate sources. For example, the two-foot tones may be used as a source of triggering signals whereas the eight-foot tones may be used as a source of signals whose wave envelopes are percussively shaped. As the-output `of yamplifier 34 is controlled by the charge on Acapacitor .30, the wav@ forni envelope of the signal appearing `across a pair iof output terminals 36 connected `to amplifier 34 `thus 'assumes 'a spaanse character corresponding to the variation in charge on capacitor 30. As the charge rises from a zero or negative state, almost immediately, to full charge then decays gradually, the resultant envelope of a signal appearing at output terminals 3o will be percussive in nature, as requirements of such an envelope are fuliilled by the selective charging of capacitor 30. Thus, the intensity envelope of output tone signals may be selectively shaped by suitably choosing the electrical values of capacitor 3d and associated time constant resistor 37.-. The output signals obtained across terminals 36 may then be passed through formant filters or other devices so as to obtain any tone color that may be desired.

It will be seen that since a pulse is created each time a signal is added to input 10, even though signals already there exist, a new charge is applied to capacitor 30 in response to activation of relay 26 upon reception of each pulse, thereby causing a percussive envelope to appear for each increment of tone added to those already existing. he novel system is thus based on a principle which utilizes the increments in D.C. voltage rather than absolute values, with each increment providing a separate pulse for operation of the envelope control amplifier 34.

Pulse amplifier 20 is a high gain amplifier and always produces a pulse much larger than is required for the operation of relay 26. Signal amplifier 12 is adapted to receive input signals several times as large as that provided by any single note before saturating or reaching a cut-out point so as to limit its output, so that for any reasonable number of notes played in sequence, a sepa- -rate percussive attack will be produced for each even though previously played keys are not released.

lt will be noted that when a previous key is held down while a second is played, the percussive wave envelope emitted by the pressing down of a certain key causes a repetition of the irst tone to appear at the output in addition to the second selected tone, since the signal for the first tone is still being applied to the envelope control amplifier 34. This result is not musically unpleasant when fully present, and, in fact, new and interesting effects are afforded by the repetition of held notes which takes place automatically. On the other hand, the player is not required to allow time for circuit recovery between the playing of one note and the next.

FIG. 2 shows in more detail by means of a schematic circuit diagram, the embodiment of the invention described in general terms above. Signal vamplifier 12 cornprising a pair of cascade connected valves 40, 42 is connected to input terminals 1i) through a potentiometer 38 whose movable arm is connected to the control electrode of valve 40. Potentiometer 38 is adjusted so that the percussion system will function properly when a tone of lowest amplitude is played and also so that a tone of vhighest amplitude has a level corresponding to a fraction of the amplifiers signal-handling capacities. Valves 40, 42 have conventional anode load resistors 44, 46 respectively and also respective cathode biasing resistors 4S, 50 with associated bypass capacitors 52, 54. Anode load resistors 44, 46 are connected to a suitable source of D.C. positivepotential 28 which may be the high voltage supply of the organ or other electronic musical instrument with which the percussion system is associated.

The tone signal applied to terminals is amplified by valve 40 and fed to valve 42 for further amplification through a coupling capacitor 56. The amplified signal is then passed to rectifier stage 14 through a coupling capacitor 5S. Rectifier state 14 has a diode 60 connected to capacitor 58 which provides half-wave rectiiication and which is also connected to a filter circuit comprising capacitors 62, 64 and resistor 66, connected in pi fashion so as to remove substantially all signal frequency ripple at the lowest frequency to be used which, for usual percussion applications, may be 120 cycles per second. The time constant of the pi filter, however, should be relatively short with respect to the highest possible tone signal repetition period with which the percussion circuit is adapted to be used. The rectifier circuit 14. also has a pair of resistors 6o, 68, 70 connected to cach electrode o of diode 6ft to provide corr ct loading thereof and areturn path for the direct current developed by rectifier 14.

Because oi the action of diode 60 and its associated pi filter, an essentially D.C. or step function wave is applied to a differentiating circuit comprising capacitor lo and l0 resistor 13 vacross which a ciamp diode '75 is connected. The output of the diierentiating circuit is in the form of -a sharp pulse which is formed when the leading edge of the step function or rectified D.C. wave is applied to the differentiating circuit. The sharp output pulse is 15 fed to a coutroi. electrode of valve 76 which forms a portion of pulse amplier 20. Valve '7S has the usual anode load resistor SG and a cathode bias resistor 82. Clamp tube 76- connected across the output of the ditierentiating circuit allows only positive going pulses to bc applied to the control electrode of valve 78.

For each positive pulse received by the control electrode or valve 7d, a negative going pulse is applied to the control electrode of valve S4 oi' relay amplifier 24, through a coupling capacitor 86. Valve 84 has a grid to ground resistor S8 and cathode bias resistor 90 whose value is suitably chosen to bias valve 8d so that sufficient current flows therethrough to maintain relay 26, normally energized and normally closed contacts 92, 94 open. Relay 26 is serially connected in the anode circuit of 30 valve 34 and it is, in turn, connected to the positive voltage source 23.

Thus, when a negative voltage appears on the control electrode of valve 84 due to reception of a positive pulse at the input of valve 78, valve 84 is driven to cut-oit and relay 26 is deenergized, thus allowing contacts 92, 94 to close. At the conclusion of the pulse received by amplifier valve '73, relay 26 is again energized and contacts 92, 94 open. Terminal 92 is connected to the junction point of voltage dividing resistors 98, which are, in turn, con- 40 nected to D.C. supply 2S, while contact 94 is connected to one terminal of capacitor 30, whose other terminal is connected to ground. Resistor 32 is connected in shunt across capacitor 30 and both of these circuit components are connected through an isolating resistor 100 to the control electrode of valve 102 of envelope control ampli- *ier 34.

The musical tone signal is fed to the control electrode of valve 102 from the output of valve 40 through a coupling capacitor 104. A'Valve 102 has the usual cathode bias resistor 106fwith a by-pass capacitor 107 connected thereacros's, and anode load resistor 10S. A coupling jcapacitor 110 is connected to valve 102 so that the output thereof is developed across a load resistor 112 which, in turn, is connected across output terminals 36.

A resistor 114 has one end connected to the positive D.C. supply and the other end connected to the cathode end of bias resistor 106 so `as to bias the tube slightly beyoud cut-ott by the voltage divider action provided by resistors 114 and, 106, as long as relay contacts 92, 94 are open. When the relay contacts are closed, due to recep- .tion of a negative pulse by relay amplifier 24, a positive voltage whose magnitude is determined by selection of Vsuitable values for voltage divider resistors 96, 98 is applied to capacitor 30, charging it substantially instanta- Aneously. At the termination of the negative impulse applied to amplifier 24, relay 26 is energized and opens contacts 92, 94, thereby allowing capacitor 30 to discharge through resistor 32. This discharge has a selected finite, exponential decay time which may be adjusted by selection of ohmic values for resistor 32.

Charging of capacitor 30 applies a voltage to a control electrode of valve 102 which opposes the bias voltage developed across cathode resistor 106. The opposing control electrode voltage is sufiicient to allow valve 102 to conduct and function normally as an amplifier so that charge the capacitor which again begins decaying.

-sgoaaess .Ascthe capacitor discharges, the control electrode voltage descends .towards Zero with a corresponding decrease .in

-anode current and similar :decrease in amplification.

There is, thus, `an almost instantaneous attack and gradual decay of tone output, producing the effect of percussion. It will thus be seen that, even though some vof Vthe previously struckfkeys are held down,'an additional note when played, will vcause another-pulse to appear at the input of amplifier 24, thereby causing the relay 26 4to Acycle and re- Thus a new percussive envelope is initiated whenever a .new

tone is played.

Although the embodiment shown in lFIG. 2 has been described in terms of negative pulses being .applied to the input relay amplifier V24, yet pulse polarity may easily be reversed by reversing .the polarity ofthe two diodes 60, 76 and by biasing valve 84 somewhat below the point of relay energization. 1f contacts 92, '94 are lchanged from normally closed 4to Vnormally open, the operation will remain the same vas'described hereinabove. However, as the amplitudes vofthe pulses applied to amplifier 24 depend on the signal amplitudes which may vary from note to note, excessive current through the relay 26 and valve 84 may.result. Therefore, generally more reliable operation is obtainable with the polarities as shown.

An additional feature of the invention is the provision of a repeat circuit so that relay 26 may be placed in continuous cyclic operation at a selected rate of speed to simulate the effect of instruments which are continuously strummed with a plectrum or the fingers or struck by hammers. This is provided by resistor 116, switch 118, capacitor 120 which are serially connected between the input of valve 7S and the output of valve 34. When switch 118 is closed, a positive feed-back is introduced between valves 78 and 84 which produces oscillations in the usual manner. The frequency of the oscillation may be controlled by suitably selecting values for resistor 116, and capacitor 12), with a rate preferably between 3 and 5 cycles per second.

If desired, a separate oscillator may be employed to provide repetitive positive pulses for amplification by pulse amplifier 20. For example, a suitable oscillator may be a conventional gas discharge, relaxation type oscillator as shown in FIG. 2A. Serially connected between D.C. supply 28 and ground are switch 72, resistor 74, gas discharge tube 75 and resistor 79. A capacitor 77 of suitable value is connected between the junction point of resistor 74, gas discharge tube 75 and ground. When the voltage developed across capacitor 77 reaches a Value sufficient to cause tube 75 to ionize the resulting discharge, current 4passes through resistor 79 and produces a narrow pulse. This pulse voltage is applied to valve 7S, so that relay amplifier 24 is pulsed in the same fashion as described above, but repeatedly at a rate dependent upon -the time constants of the oscillator circuit. As clamping of the pulses is not necessary when the oscillator circuit is used, a normally closed switch 73, gauged to switch 72 lis provided. Switch 73 disconnects the output from diode 76 when switch 72 is closed.

A modification of the present invention is shown in FIG. 3 wherein envelope control amplifier valve 102 is utilized to discharge the tone envelope shaping capacitor. This feature provides for a lengthening of the duration of the tone at a low level in order to add more realism when simulating instruments such as a piano or guitar, which have a fast initial decay but whose tones last a comparatively long time at a low level..

Components shown in FIG. 3 which are identical with those previously shown and described are given like reference numerals.

In the modification shown in FIG. 3, instead of being connected to a source of positive voltage at all times, an anode load resistor 122 is connected to the positive volt age supply 2S through relay contacts 92, 94 which remain open as long asrelay .26 `is energized. .A decay `timing .capacitor;12'4, connected to the junction point between load resistor 122 and a second ,load resistor 126, is provided `so that the decay time constant may be adjusted.

In operation, lwhen Va negative pulse is received by relay amplifier 424, relay 126 `is deenergized, thereby allowing contacts 92, 94 to close and apply a suitable positive -voltage to capacitor 124. :Capacitor 124 Vis charged substantially instantaneously and a wpositive voltage is applied to the anode of valve 102, thus allowing the signal to be amplified and passedzto output terminals 36. When relay 26 is again :energized atthe termination of the negative impulse, the positive voltage is removed from capacitor .124 and the capacitor discharges through resistor 126 and'valve 102. AIn Vthis manner, the extended time, during which the valve conducts, is achieved. The control electrode of valve 102 is placed at a slight positive potential by means of a connection to voltage dividing resistors 138, 141)` to `prevent any 'small leakage of signal from the control electrode 'to anode which would yotherwise occur after the signal decay is completed.

Another embodiment of the .invention which .is adaptable `to electrical musical instruments when it is deslred `to include `the percussion system as an `integral part Iof the entire .electronic `device is .shown .in FIG. 4. With this system the components comprising the signal amplifier 12, rectier 14, and pulse amplifier 20- may be omitted. On the other hand, a switch must be provided for each ot the keys of the instrument in order to switchably apply an actuating voltage to relay amplifier 24.

In more detail, the embodiment shown in FIG. 4 has a plurality of single pole, single throw switches 132, each of which is associated with a key of the instrument. One

' contact of all of the switches is connected in common and, in turn, this common connection is connected to a selected point on a voltage divider 133 which comprises resistors 134, 136, 138 serially connected between the positive Voltage supply and ground. Each of the other contacts of switch 132 is connected to an individual resistor which, in turn, has its other terminal connected to like terminals of the other resistors 140. These parallel connected resistor terminals are connected to a second point on voltage divider 133 and may be connected across resistor 136. The transient voltage developed across resistor V138 is applied, upon the closing of one or more of switches 132, to a collector bus 139, through a series capacitor 142, and to the control electrode of valve 84. The voltage divider network 133 is shown for purposes of illustrating a suitable means for supplying a D.C. voltage to each key switch, and it will be understood that any other suitable source of voltage, such as a small battery associated with each key, may be employed and switchably applied to collector bus 139.

The remainder of the circuit is the same as previously described in connection with FIG. 2.

`In operation, whenever a key is pressed, the resistor associated with the switch actuated by the selected key is applied in parallel across resistor 136, thereby causing the current flowing through resistor 138 to increase and develop a like increase in the voltage appearing at the ungrounded end of resistor 138. Because of the capacitor 1742 connected thereto, only the transient changes in this vo-ltage are applied to relay amplifier 24. These changes in voltage then actuate relay amplifier 24 and associated circuits in substantially the same manner as the output of pulse amplifier 20. inasmuch as the voltage change applied to the capacitor is essentially the same for every note, a positive change is indicated in FIG. 4 and the contacts of relay 26 are therefore arranged to be normally open with the relay being actuated only upon receipt of a pulse from voltage divider 133. Of course, it will be understood that relay 26 may operate in the same manner as shown and described in FIG. 2 by applying a negative voltage from supply 28 to voltage divider 133. In this case the contacts of relay 26 would be normally closed and valve 84 would be maintained in a conductive condition until a negative pulse was received by its control electrode.

While the present invention has been disclosed by means of specific illustrative embodiments thereof, it would be obvious to those skilled in the art that various changes and modifications in the means of operation described or in the apparatus, may be made without departing from the spirit of the invention as defined in the appended claim. v

The inventor claims:

In an electrical musical instrument having musical tone signal producing means, the combination comprising: a first amplifier for said tone signals; means for coupling said first amplifier to said tone signal producing means; means for normally biasing said first amplifier below cut-olf; means responsive to an actuating pulse for biasing said first amplifier above cutoff' and, after said actuating pulse has terminated, for gradually returning the bias of said first amplifier to a value below cut-off; means for generating said actuating pulse comprising a second amplifier for said tone signals, means for coupling said second amplifier to said tone producing means, means for rectifying signals amplified by said second amplifier to produce a D.C. voltage proportional to the output of said second amplifier, means for sensing changes in the level of said DC. voltage and for producing a voltage proportional to said changes, and means for amplifying positive changes so sensed to produce said ac tuating pulses; and said second amplifier adapted to opcrate below saturation with respect to a signal level in said musical tone signal producing means corresponding to the simultaneous presentation of a plurality of musical notes; whereby the presentation of any note whether played in a succession of notes or played in legato form increases the signal level to said second amplifier, creates said actuating pulse, and biases said first amplifier above cut-off.

References Cited in the file of this patent UNITED STATES PATENTS 2,301,871 Hanert Nov. l0, 1942 2,310,429 Hanert Feb. 9, 1943 2,340,001 McKellip Jan. 25, 1944 2,543,628 Hanert Feb- 27, 1951 2,793,554 Faust May 28, 1957 2,818,762 Anderson et al. Ian. 7, 1958 2,828,659 Hanert Apr. 1, 1958 

